Various analog to digital converter topologies are known. One converter topology is that of a pipeline converter. In such an arrangement the analog to digital converter is divided into a plurality of stages, each including an analog to digital converter, and each is responsible for processing an individual part of the result. Such an arrangement is shown in FIG. 1 where a pipeline analog to digital converter, generally designated 10, comprises a first stage 11 which includes a first analog to digital converter 12 and a second stage 13 which includes a second analog to digital converter 14. The first analog to digital converter 12 receives an input signal Vin at an input node 16 and creates a digital approximation of this input signal of which it derives the first M bits B1 to BM of a conversion result. There will, naturally, be an error between the actual input value Vin and the corresponding digitised value B1 to BM as derived by a digital to analog converter provided within the analog to digital converter 12. This error between the analog input signal Vin and the corresponding analog representation of the digital result VDAC1 is output as a residue at a residue output 20 of the first analog to digital converter 12. In order to facilitate the operation of the second analog to digital converter 14 which converts the lower order bits BN to BLSB where LSB represents the least significant bit, the residue is acted on by an amplifier 30 interposed between the residue output of the first analog to digital converter 12 and a signal input 32 of the second analog to digital converter 14.
The provision of the amplifier 30, which is generally known as a residue amplifier, means that the magnitude of the input signal to the second analog to digital converter 14 is much increased, thereby simplifying the design of the second analog to digital converter and improving its performance in terms of signal to noise ratio.
The pipeline converter topology also allows an increase in digital throughput. Thus, for example, whilst the second analog to digital converter 14 is converting the least significant bits BN to BLSB of a Dth word, the first analog to digital converter 12 can be converting the most significant bits B1 to BM of a D+1th conversion. As such it remains an important topology.